Permanent magnet rotor assembly having rectangularly shaped tongues

ABSTRACT

A rotor assembly having a hub with rectangularly-shaped tongues and wedge-shaped permanent magnets.

CROSS REFERENCE TO RELATED APPLICATIONS

This invention relates to subject matter disclosed in concurrently filedpatent application Ser. No. 973,346, by Alexander Silver, Frederick B.McCarty, entitled "Wedge-Shaped Permanent Magnet Rotor Assembly"; Ser.No. 973,345, by Jerry Glaser, entitled "Rotor Assembly Having AnchorsWith Undulating Sides"; and Ser. No. 973,343, by Alexander Silver,Frederick B. McCarty and Lyman R. Burgmeier, entitled, "Rotor AssemblyWith Magnet Cushions".

BACKGROUND OF THE INVENTION

This invention relates to permanent magent rotor assemblies, and moreparticularly, to rotor assemblies having a hub with rectangularly shapedtongues and wedge-shaped permanent magnets.

In the art, methods have been developed to join the non-magnetic hub tothe magnetic pole pieces in a rotor assembly. One such method is the hotisostatic pressure (HIP) bonding process which is performed underextreme pressure (circa 18,000 p. s. i. a.) and at elevated temperatures(circa 2200° F.). Another method used to join the non-magnetic andmagentic rotor materials together is furnace brazing, which is alsoperformed at elevated temperatures (circa 1860° F.). The elevatedtemperatures of either the HIP bonding or the brazing techniques reducethe strength of the two dissimilar metals, which is very undesirable ina high speed rotor where the strength of the rotor's components are ofgreat importance.

SUMMARY OF THE INVENTION

The permanent magnet rotor assembly, in accordance with the invention,includes a rotatable hub with a plurality equally spaced radiallyprojecting tongues or spokes disposed around the outer periphery of thehub. The rotor assembly also includes inwardly converging wedge-shapedsupport members each having a central groove to fit over the tongueprojecting from the hub to form an outwardly converging wedge-shapedopening between adjacent support members. The rotor assembly furtherconsists of a plurality of outwardly converging wedge-shaped permanentmagnets which are positioned in the openings formed between adjacentsupport members and which provide wedging action to squeeze the supportmembers against the tongues.

A principal advantage of the present invention is that since the wedgingaction of the wedge-shaped magnets presses the support members andtongues together, a brazing alloy with a lower melting temperature thanpreviously used brazing materials can be used to join the two materials.Because lower temperatures are used, the rotor assembly materials losevery little of their properties, such as their strength.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-section view of the rotor assembly of the presentinvention with tangenially magnetized magnets.

FIG. 2 shows a two-section support member.

FIG. 3 is a variation of FIG. 1, whereby the magnets are radiallymagnetized.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1, a permanent magnet rotor assembly 10 includes asubstantially cylindrical hub 12 with a plurality of equally spacedrectanguarly shaped tongues 14 extending around the periphery thereof.Disposed between each pair of adjacent tongues 14 on the outer peripheryof the hub 12 is a recess 16. In the tangentially magnetizedconfiguration of FIG. 1, the hub 12 consists of a non-magnetic material.

A plurality of inwardly converging wedge-shaped support members 18, eachhaving a groove 20, are positioned around the hub 12 such that thegrooves 20 interlock with the tongues 14. The groove 20 generallycomprises a rectangular slot 21 which opens to a circular hole 22. Therectangular slot 21 of the support members 18 fits over the tongues 14.The circular hole 22 of the groove 20 reduces the rotor's mass andallows air to flow through the rotor assembly 10 and to reduce thesurface temperature of the assembly. Also, the hole 22 creates aflexible beam at 23 which allows the support members 18 to adjust theirwedge angles. The support members 18 consist of a ferromagnetic materialwhen tangentially magnetized magnets are used.

When the inwardly converging wedge-shaped support members 18 areinterlocked with the tongues 14, the equally spaced support members formoutwardly converging wedge-shaped openings 24 therebetween.

While the support member 18 is shown as a single piece construction inFIG. 1, an alternative support member consisting of two substantiallytriangularly shaped sections 25 and 26 with semicircular recesses 27 and28 respectively can be utilized as shown in FIG. 2. The two section 25and 26 which are much easier to fabricate can be joined by brazing themtogether at a junction 30.

The support members 18 of FIG. 1 and 2 are joined to the hub 12 bybrazing the sides of the tongues 14 to the straight sides of the slot 21of the support members 18. The brazing of the support members 18 to thetongues 14 can be performed in the 1150-1200° F. temperature range.Since this range of temperatures is relatively low, there is little lossof properties in the magnetic support member material.

Outwardly converging wedge-shaped permanent magnets 32 are located inthe openings 24 between the support members 18. The magnets 32 areshorter in length than the distance from the base of the recess 16 tothe outer periphery of the rotor assembly 10 thereby forming a gap 34between the base of the magnet 32 and the base of the recess 16. Thepurpose of the gap is to facilitate assembly, and to further cool therotor 10 by permitting cooling air to flow through the rotor assembly.

The base of the magnets 32 has slightly rounded corners 36 and 38 foreasy insertion of the magnets 32 into the openings 24.

The size of the angle formed between the sides of the magnets 32 and aplane parallel to a central radius through the magnet is critical andshould be slightly less than the angle of friction. This angle isexperimentally determined and is the maximum angle at which a lockingwedge action is achieved for the material and conditions pertinent to agiven design. If the angle is too large the magnets will not remainlocked in place after the rotor ceases to rotate and if the angle is toosmall, lateral crushing forces may cause the magnet to fracture.Therefore, there is a critical range within which the locking angle θmust lie. It has been found that the size of the locking angle θ shouldbe between 2 to 9 degrees, preferably 6 to 8 degrees.

A thin hoop 40 which is heat shrunk upon the peripheral surface of thesupport members 18 functions as an electric damper to intercept anddiminish the flux harmonics caused by the stator and penetrating intothe support members 18 and into the magnets 32. Reflecting eddy currentsare produced in the hoop 40, thereby shielding the permanent magnets 32and the support members 18. The hoop 40 has a minor structural function,providing a retaining force over the peripheral contact with the magnets32 and the support members 18. This retaining force is small and merelysupplemental to the retaining provided by the hub 12. The hoop 40consists of a high strength, non-magnetic material preferably having alow resistivity, such as a beryllium copper alloy.

The rotor assembly 10 is constructed by first sliding the rectangularportion of the slot 20 of the support member 18 onto the rectangularlyshaped spokes 14 and by then brazing the support members 18 to thespokes 14 (at about 1200° F.). Next, the magnets are inserted into thespace between the support members 18 followed by rotating the rotorassembly 10 at its maximum allowable speed. During rotation the magnetsmove radially outward due to centrifugal force. The magnets are thenlocked in place even after the rotor ceases rotating due to thecompressive forces exerted on the magnets by the walls of the supportmembers 18. Also, as centrifugal force moves the magnets radiallyoutward the wedging action of the wedge-shaped magnets compresses thebrazed joint between the support members 18 and the tongues 14 tighteras the speed of the rotor assembly increases. The outer portions of thesupport members 18 and the magnets 32 are then ground to the properdimensions and the hoop 40 is shrunk onto the periphery, thus completingthe assembly.

FIG. 3 shows a permanent magnet rotor assembly 42 which includes asubstantially cylindrical hub 44 with a plurality of equally shapedrectangularly-shaped tongues 46. The hub 44 consists of a magneticmaterial when radially magnetized magnets are used, as shown in FIG. 3.

A plurality of inwardly converging wedge-shaped support members 48 witha groove 50 are positioned to interlock with the tongues 46. The groove50 has a rectangularly-shaped slot 52 opening to a circular hole 54. Therectangular slot 52 interlocks with the tongues 46. The circular-shapedhole 54 reduces the rotor's mass and allows air to flow through therotor assembly 42 and to reduce the surface temperature of the assembly.The support member 48 consist of a non-magnetic material when radiallymagnetized magnets are used.

Outwardly converging wedge-shaped permanent magnets 56 are locatedbetween the support members 48. The magnets 56 are shorter in lengththan the distance from the hub 44 to the outer periphery of the supportmembers 48 thereby forming a gap 58 between the base of the magnet 56and the hub 44.

The gap 58 is filled with a close shim 60 which consists of aferromagnetic or permanent magnetic material. The shim 60 reduces theresistance of the magnetic path which is created by the gap 58.

The rotor assembly 10 of FIG. 3 also has dampening bars 62 which arelocated near the rotor's periphery and extend through the supportmembers 48. The bars 62 function as an electric damper to diminish theflux harmonics caused by the stator. Also, a thin hoop 64, which is heatshrunk around the peripheral surface of the support members 48 and themagnets 56 provides added electrical dampening. Alternatively, the bars62 can be used without the hoop 64.

The rotor 42 is assembled in a like manner to that of the rotor 10 ofFIG. 1, described above. But with the rotor 42, the shim 60 is insertedinto the gap 58 after the rotor has been rotated and so that the magnets56 are locked in place.

While specific embodiments of the invention have been illustrated anddescribed, it is to be understood that these embodiments are provided byway of example only and the invention is not to be construed as beinglimited thereto, but only by the proper scope of the following claims:

What is claimed is:
 1. A permanent magnet rotor assembly comprising:ahub having radially extending tongues of a uniform parallel sidedcross-section equally spaced around the outer periphery of said hub; aplurality of inwardly converging wedge-shaped support members radiallydisposed around the outer periphery of said hub, said support memberseach having an inwardly opening groove, each groove having an inneruniform parallel sided cross-section portion and an outer circularportion, the inner uniform parallel sided cross-section portionreceiving and affixed to a corresponding uniform parallel sidedcross-section radially extending tongue without the tongue extendinginto the outer circular portion of the groove, each pair of adjacentinwardly converging wedge-shaped support members forming an outwardlyconverging wedge-shaped opening therebetween; a plurality of outwardlyconverging wedge-shaped permanent magnets, individual magnets disposedin individual outwardly converging wedge-shaped openings between saidsupport members with a gap between said permanent magnets and theperiphery of said hub; during rotation of the rotor assembly theoutwardly converging wedge-shape of said permanent magnets compressingsaid support members around the tongues radially extending from saidhub.
 2. The permanent magnet rotor assembly of claim 1 wherein saidpermanent magnets are tangentially magnetized.
 3. The permanent magnetrotor assembly of claim 1 wherein said permanent magnet are radiallymagnetized.
 4. The permanent magnet rotor assembly of claim 3additionally including a plurality of shims, individual shims disposedin individual gaps between said permanent magnets and the periphery ofsaid rotor.
 5. In an electrical machine having a rotor and a stator,said rotor comprising:a hub having radially extending tongues equallyspaced around the the outer periphery of said hub; a plurality ofinwardly converging wedge-shaped support members radially disposedaround the outer periphery of said hub; said support members each havingan inwardly opening groove to receive a radially extending tongue; eachpair of adjacent inwardly converging wedge-shaped support membersforming an outwardly converging wedge-shaped opening therebetween; aplurality of outwardly converging wedge-shaped permanent magnets withradially extending outwardly converging sides located in said opening;said sides of said magnets forming an angle within the range of 2 to 9degrees with a plane parallel to a central radius through said magnetssuch that the magnets are locked in place after rotor ceases to rotateand the magnets will not fracture due to excessive compressive forcesapplied to the sides of said magnets.
 6. In an electrical machine havinga rotor and a stator, said rotor comprising:a hub radially extendingtongues equally spaced around the outer periphery of said hub; aplurality of inwardly converging wedge-shaped support members radiallydisposed around the outer periphery of said hub; said support memberseach having an inwardly opening groove to receive a radially extendingtongue; each pair of adjacent inwardly converging wedge-shaped supportmembers forming an outwardly converging wedge-shaped openingtherebetween; a plurality of outwardly converging wedge-shaped permanentmagnets with radially extending outwardly converging sides located insaid opening; said sides of said magnets forming an angle within therange of 6 to 8 degrees with a plane parallel to a central radiusthrough said magnet such that the magnets are locked in place after saidrotor ceases to rotate and the magnets will not fracture due toexcessive compressive forces applied to the sides of said magnets.
 7. Apermanent magnet rotor assembly comprising:a hub having radiallyextending tongues equally spaced around the outer periphery of said hub;a plurality of inwardly converging wedge-shaped support members radiallydisposed around the outer periphery of said hub, said support memberseach having an inwardly opening groove affixed around and to a radiallyextending tongue and each pair of adjacent inwardly convergingwedge-shaped support members forming an outwardly convergingwedge-shaped opening therebetween; and a plurality of outwardlyconverging wedge-shaped permanent magnets with radially extendingoutwardly converging sides disposed in said opening; said sides of saidmagnets forming an angle within the range of 2 to 9 degrees with a planeparallel to a central radius through said magnets such that duringrotation of the rotor the wedge-shaped magnets will compress the supportmembers around the tongues radially extending from said hub.
 8. Apermanent magnet rotor assembly comprising:a hub having radiallyextending tongues equally spaced around the outer periphery of said hub;a plurality of inwardly converging wedge-shaped support members radiallydisposed around the outer periphery of said hub, said support memberseach having an inwardly opening groove affixed around and to a radiallyextending tongue and each pair of adjacent inwardly convergingwedge-shaped support members forming an outwardly convergingwedge-shaped opening therebetween; and a plurality of outwardlyconverging wedge-shaped permanent magnets with radially extendingoutwardly converging sides disposed in said openings; said sides of saidmagnets forming an angle within the range of 6 to 8 degrees with a planeparallel to a central radius through said magnets such that duringrotation of the rotor the wedge-shaped magnets will compress the supportmembers around the tongues radially extending from said hub.